*shrug*... to each their own, I guess. Personally, I don't plan on buying a dry suit, and that's for BC waters. But hey... that's just me.
I would be inclined to suggest the same reasons for going for the reg/BC first -- it means you get to try out some different exposure suits and find one you like. And save up for a really nice one if you want to.
As jonnythan said -- for the most part, a reg is a reg. So, you try a couple out before purchase and find one that you like. Try out the AquaLung comfobite mouthpiece -- some love it, others hate it. Try out something else. Then buy.
As for BC's... there are a lot of people here that swear by a BP/wing. It's more of a cult than anything else, it seems. When asked to give qualitative or quantitative reasons as to why it is better they often say "it just is, ok?" -- dive with what you like and don't let anyone push you into DIR.